Syntheses, Molecular Structures, and Spectroscopy of Gold(III) Dithiolate Complexes.

Abstract

Two Au(III) dithiolate complexes, [Au(dbbpy)(tdt)]PF(6) and Au(eta(2)-C,N-ppy)(tdt), (dbbpy = 4,4'-di-tert-butyl-2,2'-bipyridine; tdt = 3,4-toluenedithiolate; ppy = C-deprotonated 2-phenylpyridine), have been prepared and structurally characterized by X-ray crystallography. The complexes have low-energy absorption bands that exhibit mild solvatochromism (lambda(max) = 444 nm (epsilon, 2310 M(-)(1) cm(-)(1)) in CH(2)Cl(2) and 406 nm (epsilon, 3170 M(-)(1) cm(-)(1)) in DMSO) and are tentatively assigned to a charge-transfer-to-diimine transition. This transition occurs at higher energy than the analogous charge-transfer transition in related Pt(II) complexes (e.g., Pt(dbbpy)(tdt), lambda(max) = 563 nm (epsilon, 7200 M(-)(1) cm(-)(1)). Whereas neither Au(III) complex is emissive, their respective dichloride precursors, [Au(dbbpy)Cl(2)]PF(6) and Au(eta(2)-C,N-ppy)Cl(2), luminesce in low-temperature glass matrixes from an excited state that is tentatively assigned as intraligand pi-pi. The neutral complex, Au(eta(2)-C,N-ppy)(tdt), is more easily oxidized (E(ox) = 0.925 V vs 1.589 V (vs NHE)) and less easily reduced (E(red) = -1.339 V vs -0.255 V (vs NHE)) than the cationic complex, [Au(dbbpy)(tdt)]PF(6). Both dithiolate complexes exhibit approximately square planar coordination. Yellow crystals of [Au(dbbpy)(tdt)]PF(6) (C(25)H(30)AuF(6)N(2)PS(2)) are triclinic, space group P&onemacr; (No. 2), with a = 7.1977(2) Å, b = 11.7292(1) Å, c = 17.5820(5) Å, alpha = 104.537(2) degrees, beta = 96.592(2) degrees, gamma = 102.455(2) degrees, V = 1380.41(6) Å(3), Z = 2, and final R = 0.050 (R(w) = 0.1062) for 3446 unique reflections. Orange crystals of Au(eta(2)-C,N-ppy)(tdt) (C(18)H(14)AuNS(2)) are monoclinic, space group P2(1)/c (No. 14), with a = 8.852(1) Å, b = 11.726(2) Å, c = 15.499(5) Å, beta = 101.34(2) degrees, V = 1577.5(6) Å(3), Z = 4, and final R = 0.0438 (R(w) = 0.0759) for 3685 unique reflections. A structural trans effect in Au(eta(2)-C,N-ppy)(tdt) results in a significantly longer Au-S distance (ca. 0.1 Å) trans to the Au-C bond than that trans to the Au-N bond. In the solid state, the [Au(dbbpy)(tdt)](+) cations are arranged in stacks with alternating intermolecular Au.Au separations of 3.60 and 3.75 Å while the Au(eta(2)-C,N-ppy)(tdt) molecules form stacks with an intermolecular Au.Au separation of 3.81 Å.